Refractory powder hot-pressing system

ABSTRACT

A system for hot-pressing refractory powders into dense sintered bodies comprises a tunnel type furnace having a given temperature distribution therein, a plurality of die assemblies each of which has a refractory powder sandwiched between an upper punch and a lower punch thereof, a plurality of supporters for said plurality of dies. At least one pressing means is positioned at a given position in the tunnel type furnace to be at a given temperature. Means are provided for conveying said supporters intermittently one by one from an inlet of said tunnel type furnace through said at least one pressing means to an outlet of said tunnel type furnace, whereby the refractory powder in each of said die assemblies is hot-pressed into a dense sintered body by said at least one pressing means and the dense sintered bodies are conveyed to said outlet. The equipment is suitable for massproduction of hot-pressed bodies of materials such as ferrites and ferroelectric oxides.

United States Patent 1 1 Chiba et al.

1111 3,713,193 1451 Jan. 30, 1973 REFRACTORY POWDER HOT- PRESSING SYSTEMInventors: l-liroyuki Chiba, Neyagawa; Hideaki Masuda, Moriguchi; EiichiHirota, Sakai, all of Japan Matsu shita Electric Industrial Co., Ltd.,Osaka, Japan Filedt Oct. 12,1970

Appl. No.2 79,871

[73] Assignee:

Foreign Application Priority Data Oct. 21, 1969 Japan ..44/84524 [52]US. Cl ..25/132,25/135, 25/142 R, 25/142 M, 264/332 Eiel dofS earch.....-..L ..@1125/142M, 142 D, 135 Z, 142 F,l32,142'R,134;

[56] v References Cited UNITED STATES PATENTS 2/1967 King .;l8/l6.5 X1/1971 Alliegro... ....l8/l6.5 X 3/1967 Pietsch 8/1938 H1925Ridgway...,.. McIntosh ..25/l32 X 1m. 01 ..F27b 9/02 FOREIGN PATENTS ORAPPLICATIONS 516,858 1/1931 Germany ..25/l42 F Primary Examiner-J.Spencer Overholser Assistant Examiner-Ben D. Tobor Att0rneyWenderoth,Lind & Ponack [57] ABSTRACT A system for hot-pressing refractory powdersinto dense sintered bodies comprises a tunnel type furnace having agiven temperature distribution therein, a plurality of die assemblieseach of which has a refractory powder sandwiched between an upper punchand a lower punch thereof, a plurality of supporters for said pluralityof dies. At least one pressing means is positioned at a given positionin the tunnel type furnace to be at a giyen temperature. Means areprovided for conveying Said supporters intermittently one by one from aninlet of said tunnel type furnace through said at least one pressingmeans to an outlet of said tunnel type furnace, whereby the refractorypowder in each of said die assemblies is hot-pressed into a densesintered body by said at least one pressing means and the dense sinteredbodies are conveyedto said outlet. The equipment is suitable formass-production of hotpressed bodies of materials such as ferrites andferroelectric oxides.

V 8 Claims, 3 DrawingFigures PATENTEDJAN 30 1915 v 3,713,193

SHEET 1 BF 3 FIG! ' HIROYUKI CHIBA,

HIDEAKI MASUDA and EIICHI HIROTA,

% INVENTOR BY 144.0% fizz #2 4! ATTORNEYS PAIENTEDJMO ma 3.713; 193

sum 2 or 3 33 fiL 34 FIG- 2 HIROYUKI CHIBA,

HIDEAKI MASUDA and EIICHI HIROTA,

INVENTORS ATTORNEYS PATENTED JAN 30 I973 SHEET 3 BF 3 HIROYUKI CHIBA,

HIDEAKI MASUDA & EIICHI HIROTA,

INVENTOR REFRACTORY POWDER HOT-PRESSING SYSTEM BACKGROUND OF THEINVENTION This invention relates to a system for hot-pressing refractorypowders into dense sintered bodies. More particularly, the inventionrelates to an improved hotpressing system suitable for themass-production of dense sintered bodies.

I-leretofore, refractory powders such as oxides, nitrides, carbides ormixtures thereof, were hot-pressed by using a system comprisinghot-pressing dies, pressing means and a furnace. The refractory powderwas heated in the dies up to an elevated temperature, hot-pressed into adense sintered body and thereafter, cooled to room temperature.

Such prior hot-pressing system is, however, capable of producing onlyone pressed body during a single cycle which took a long period of time.Therefore, such systems are unsuitable for the mass-production ofhotpressed bodies. of

Hot-press sintering is a well-known method for producing a densesintered body having a controlled microstructure, a low porosity andfine or large grains. Thus, it is necessary to adjust the hot-pressingoperating conditions such as heating temperature, time period andmagnitude of pressure. Therefore, a suitable hotpressing system must becapable fo controlling these hot-pressing operating conditions.

Especially, in the hot-pressing of a magnetic oxide such as ferrite,these conditions must be carefully controlled to obtain a sinteredferrite body having both low porosity and excellent electro-magneticproperties.

OBJECTS AND BRIEF DESCRIPTION OF THE INVENTION It is an object of thepresent invention to provide a novel hot-pressing system for themass-production of dense sintered bodies by hot-pressing refractorypowder.

It is another object of the present invention to provide a novelhot-pressing system capable of controlling hot-pressing operatingconditions.

A further object of the present invention is to provide anovelhot-pressing system capable of hotpressing a magnetic oxide such asferrite materials.

A still further object of the present invention is to provide a novelsystem capable of hot-pressing ferroelectric oxide materials, such asbarium titanate, lead zirconate titante and mixtures thereof.

These objects are achieved by providing a hotpressing system forhot-pressing refractory powders into dense sintered bodies comprising atunnel type furnace having a given temperature distribution therein, aplurality of die assemblies each of which has a refractory powdersandwiched between an upper punch and a lower punch thereof, a pluralityof supporters for said plurality of dies, at least one pressing meanswhich is positioned at a given position within said tunnel type furnaceat a given temperature, and means for conveying said supportersintermittently one by one from an inlet of said tunnel type furnacethrough said at least one pressing means to an outlet of said tunneltype furnace, whereby the refractory powder in each of said dieassemblies is hot-pressed into a dense sintered body by said at leastone pressing means and the dense sintered bodies are conveyed to saidoutlet.

Other and further features and advantages of the invention will appearfrom the following description of a preferred embodiment thereof, takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view partially incross-section of a hot-pressing system according to the presentinvention;

FIG. 2 is a cross-sectional view taken along line "-11 of FIG. I; and

FIG. 3 is a perspective and cross-sectional view of a hot-pressing dieassembly mounted on a supporter in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1 referencecharacter 1 designates, as a whole, a hot-pressing system including atunnel type furnace 2 which can be adjusted to have a desiredtemperature distribution therein. Pressing devices 3 and 3' arepositioned at given positions of the tunnel type fumace' 2, and aremovable to various desired positions. A plurality of die assemblies 4,each of which has at least one type of refractory powder 5 insertedtherein, are mounted on a plurality of supportors 6 and areintermittently pushed by a pusher 7 and conveyed one by one from aninlet 8 of the tunnel type furnace 2 through pressing devices 3 and 3 toan outlet 9 of the tunnel type furnace 2, The refractory powders 5 ineach of the die assemblies 4 are hot-pressed into a dense sintered bodyby the pressing devices 3 and 3. The dense sintered bodies are thenconveyed to outlet 9 without pressure. 1

In accordance with the present invention the tunnel type furnace 2 isdivided into a plurality of rooms 10 by heat insulating walls 11 each ofwhich has, a cut-off 12 to allow the die assemblies 4 on supporters 6 topass therethrough as shown in FIGS. 1 and 2. Each of the plurality ofrooms 10 have heaters 13 and heat reflecting plate 14 made of firebricks. It is important that each of the plurality of rooms 10 have agiven temperature and a substantially uniform temperature distributiontherein, thus each of the rooms 10 tend to form separate temperaturezones. Rooms 10 have a length substantially equal to each other alongthe length of travel of theplurality of supportors 6. The insulatingwalls 11 assure a homogeneous temperature distribution in each of therooms 10.

According to the present invention the plurality of supporters 6 aresubstantially equal in length and also substantially equal to saidlength of rooms 10. Each of the supporters 6 is pushed by a pusher 7 andconveyed intermittently by a distance substantially equal to ntimes thelength of the rooms 10, n being an integer including one. After beingconveyed by this distance, the supporters 6 stop for a given time periodand are then conveyed further. Such movement is repeated throughout thefurnace 22. It is important that each of the supporters 6 be locatedexactly in each room 10 and not be stopped across two of the rooms 10.Otherwise, the hot-pressing die assemblies 4 in which refractory powdersare placed are heated unequally between the two adjacent roomshavingdifferent temperatures.

This causes cracking of the die assemblies 4 and prevents thesatisfactory hot-pressingof the refractory powders.

Referring to F IG. 2 the pressing device 3 comprises a hydraulic oilcylinder 15, a lower movable cylinder 16,

' an upper stationary cylinder 18, and a frame 19 and is installed inone of the rooms 10.

It is preferable that the pressing device 3 be easily moved to a desiredroom as desired according to the hot-pressing schedule. For this purposetunnel type furpreferably and essentially of first pressing device 3 anda second pressing device 3,'whereby the first pressing device 3 ispositioned in a room of lower temperature than that of the second:pressing device. It is desirable that the first pressing device 3 havean upper stationary cylinder 18 positionedat a lower level than an upperstationary cylinder 18' of the second pressing device. This arrangementprevents a collision of the upper stationary cylinder 18' with the upperpunch of a die assembly when said die assembly is conveyed to a roomwhere the pressing device is installed.

Referring to F IG. 3, a die assembly 4 is mounted on a supporter 6 whichhas a heat insulating refractory plate 20 at the top thereof in order toprevent the heat from flowing to the bottom of supporter-6. Each of thesupporters 6 has a movable refractory plunger 21 for transmitting apressing force from pressing device 3 to the lower punch 23 of the dieassembly 4. According to the present invention, the refractory plunger21 consists es- .sentially of two blocks 24 and 25. Block 24 is made ofrefractory material such as Sic, Si N and mixtures thereof or A1 andismovably inserted in a guide 26 provided in said heat insulatingrefractory plate 20. Block 24 has an upper flange 24a thereon whichabuts the top surface of refractory plate 20. Block 25 is made of heatresistantmaterial, such as heat-resisting steel,

and has a heat insulating layer 27 made of material such as asbestosbetween the top portion 250 and the bottom portion 25b thereof. Thisinsulating layer 27 prevents the heat from flowing to the lower portionof block 25. I

Die assembly 4 comprises at least a die 28, a lower punch 23 and anupper punch 29 made of a refractory material. The refractory materialmust have a good heat conductivity and high mechanical strength atdesired hot-press temperatures. Preferable materials for die assembly 4are refractory oxides such as Al,O ZrO, or SiC, Si N and mixturesthereof. According to the present invention dieassembly 4 is placed on aholder 30 made of the above-mentioned preferable refractory materialwhich is then positioned on the upper surface of refractory plate 20.Holder 30 has a hole 31 formed at the center thereof, through whichlower punch 23 and the top portion of block 24 move without moving die28 upon application of force from pressing device 3. Die assembly 4 ispreferably surrounded by a refractory cylinder 32 made of a materialhaving good heat conductivity to equalize the temperature distributionthroughout the die assembly 4 and the refractory powder 5. It ispreferable to use a material such as A1 0, and SiC for cylinder 32.

Previously cold-pressed refractory powders are placed in die 28 andsandwiched between lower punch 23 and upper punch 29. Refractory powders5 are Cally, lower movable cylinder 16 of pressing device.3 is, movedupwardly by hydraulic oil cylinder and thus preferably enveloped withpowder 50 of material such as A1 0 and ZrO within die 28. Thisenveloping powder protects the refractory powders from a reaction withthe die material. According to the present invention, supporters 6 havewheels 34 which are movable along rails 33 laid on the bottom of tunneltype furnace 2 by the action of pusher 7. Thus, the supporters 6 can besmoothly moved, even while carrying the heavy die assembly, holder,refractory plate and plunger.

The refractorypowder 5 is conveyed into the room 10 having pressingdevice 3, and is hot-pressed. Specifilifts refractory plunger 21, whichpresses die assembly 4 having refractory powder 5 therein against upperstationary cylinder 18 for a desired time period while supporter 6 isstopped. After hot-pressing, lower movable cylinder 16 moves downwardly,and therefore, die assembly 4 is again moved downwardly onto holder 30.

Thereafter, die assembly 4 on supporter 6 is conveyed to the next room10 by means of pusher 7.

According to the present invention refractory powder 5 is preferably amolded powder of a ferromagnetic oxide or of a ferroelectric oxide suchas ferrites, barium-titanate and lead-zirconate titanate.

ln the case of a ferromagnetic or ferroelectric oxide material, a densesintered body having a porosity lower than 0.5 percent is obtained byhot-pressing at a temperature ranging between 1000 C and 1500 C and apressure higher than 50 kg/cm, regardless of theoxide composition. Inthis case, block 24, die 28, lower punch 23 and upper punch 29 arepreferablymade of SiC or Si N or a mixture thereof, because thesematerials have a high mechanical strength at temperatures of from 1000 Cto 1500 C. The refractory cylinder 32 and the holder 30 are alsopreferably made by SiC or Si N or a mixture thereof, because thesematerials have high' heat conductivity.

An example of a use of the system of the present invention is describedas follows. This example is meant to be illustrative of a preferred useof the invention, and is not meant to limit the scope thereof.

Mixtures of 24 percent MnO, 24 percent ZnO, 52 percent Fe O all percentsbeing mole percents, where molded into" discs each having a diameter ofmm and a thickness of 30 mm. These molded ferrite bodies were placedinto a hot pressing die made of a mixture of SiC and Si N The die had anouter diameter of 240 mm and an inner diameter of mm and a height of l00mm. The molded ferrite bodies were enveloped in A1 0, powder in order toprevent a reaction of the fer-, rite with the die material and to presshomogeneously throughout the molded ferrite body. The hot pressingsystem had two press devices which were installed at furnace roomshaving temperatures of l200 C and of 1350 C, respectively. The moldedferrite bodies were treated by the two stage hot-press process atconditions of 250 ltg/cm at l200 C and 350 ltg/cm at 1350 C. The dieswere conveyed intermittently into the next furnace room at an intervalof 30 minutes.

The obtained ferrite bodies had a weight of about 1 kg, a porosity lowerthan 0.5 percent and an initial permeability of 20,000L2000 at l KHz.The ferrite bodies were composed of grains which were larger than Whatis claimed is:

l. A system for hot-pressing refractory powders into dense sinteredbodies, said system comprising a tunnel type furnace having an inlet andan outlet and a given temperature distribution therein; a plurality ofdie assemblies, each of which has said refractory powders sandwichedbetween an upper punch thereof; a plurality of supporters for saidplurality of die assemblies, each of said plurality of supporters havinga refractory plate at the top thereof in order to prevent the bottom ofsaid supporter from being heated and having a refractory plunger movablyinserted in a guide thereof and extending through and abutting the topsurface of said refractory plate, whereby a pressing force from saidpressing means is transferred through said plunger to said lower punch;at least one pressing means which is positioned at a given positionhaving a predetermined temperature within said tunnel type furnace;means for conveying said supporters intermittently one by one from saidinlet, through said at least one pressing means to said outlet; wherebysaid refractory powders in each of said die assemblies are hot-pressedinto a dense sintered body by said at least one pressing means and saiddense sintered body is conveyed to said outlet.

2. A system as claimed in claim 1, wherein said plurality of supportersare substantially equal in length to each other along the path of travelthrough said furnace, and each of said supporters isconveyedintermittently by a distance substantially equal to mtimes saidlength, n being an integer including one.

3. A system as claimed in claim 2, wherein said tunnel type furnace isdivided into a plurality of rooms by insulating walls, each of which hasa cut-off to allow said die assemblies on said supporters to passtherethrough, said plurality of room having a length substantiallysimilar to said length of said supporters.

4. A system for hot-pressing refractory powders into dense sinteredbodies, said system comprising a tunnel type furnace having an inlet andan outlet and a given distribution of difi'erent temperature zonestherein; a plurality of die assemblies, each of which has saidrefractory powders sandwiched between an upper punch and a lower punchthereof; a plurality of supporters for said plurality of die assemblies;at least one pressing means which is positioned at a given positionhaving a predetermined temperature within said tunnel type furnace, saidat least one pressing means comprising a first pressing device and asecond pressing device, said first and second pressing devices beingpositioned within different temperature zones of said furnace.

5. A system as claimed in claim 4, wherein each of said pressing deviceshave upper stationary cylinders, said upper stationary cylinder of saidfirst pressing device being positioned at a lower level than said secondpressing device.

6. A system as claimed in claim 1, wherein said refractory plungercomprises two blocks, one of which is made of refractory material andthe other of which is made of heat resistance material.

7. A system as claimed in claim 1, wherein each of said die assembliesincludes a die, and further comprising a holder positioned on said topsurface of each of said refractory plates, said holder having a holeformed at the center thereof, said die being positioned on said holder,whereby said lower punch and the top portion of said plunger moveupwardly through said hole without moving said die upon application ofpressure force from said pressing means.

8. A system as claimed in claim 1, wherein each of said plurality of dieassemblies is surrounded by a refractory cylinder.

1. A system for hot-pressing refractory powders into dense sintered bodies, said system comprising a tunnel type furnace having an inlet and an outlet and a given temperature distribution therein; a plurality of die assemblies, each of which has said refractory powders sandwiched between an upper punch thereof; a plurality of supporters for said plurality of die assemblies, each of said plurality of supporters having a refractory plate at the top thereof in order to prevent the bottom of said supporter from being heated and having a refractory plunger movably inserted in a guide thereof and extending through anD abutting the top surface of said refractory plate, whereby a pressing force from said pressing means is transferred through said plunger to said lower punch; at least one pressing means which is positioned at a given position having a predetermined temperature within said tunnel type furnace; means for conveying said supporters intermittently one by one from said inlet, through said at least one pressing means to said outlet; whereby said refractory powders in each of said die assemblies are hot-pressed into a dense sintered body by said at least one pressing means and said dense sintered body is conveyed to said outlet.
 2. A system as claimed in claim 1, wherein said plurality of supporters are substantially equal in length to each other along the path of travel through said furnace, and each of said supporters is conveyed intermittently by a distance substantially equal to n-times said length, n being an integer including one.
 3. A system as claimed in claim 2, wherein said tunnel type furnace is divided into a plurality of rooms by insulating walls, each of which has a cut-off to allow said die assemblies on said supporters to pass therethrough, said plurality of room having a length substantially similar to said length of said supporters.
 4. A system for hot-pressing refractory powders into dense sintered bodies, said system comprising a tunnel type furnace having an inlet and an outlet and a given distribution of different temperature zones therein; a plurality of die assemblies, each of which has said refractory powders sandwiched between an upper punch and a lower punch thereof; a plurality of supporters for said plurality of die assemblies; at least one pressing means which is positioned at a given position having a predetermined temperature within said tunnel type furnace, said at least one pressing means comprising a first pressing device and a second pressing device, said first and second pressing devices being positioned within different temperature zones of said furnace.
 5. A system as claimed in claim 4, wherein each of said pressing devices have upper stationary cylinders, said upper stationary cylinder of said first pressing device being positioned at a lower level than said second pressing device.
 6. A system as claimed in claim 1, wherein said refractory plunger comprises two blocks, one of which is made of refractory material and the other of which is made of heat resistance material.
 7. A system as claimed in claim 1, wherein each of said die assemblies includes a die, and further comprising a holder positioned on said top surface of each of said refractory plates, said holder having a hole formed at the center thereof, said die being positioned on said holder, whereby said lower punch and the top portion of said plunger move upwardly through said hole without moving said die upon application of pressure force from said pressing means. 